The present disclosure relates to a solid-state imaging device and an electronic apparatus including the solid-state imaging device.
Hitherto, as solid-state imaging devices, complementary metal oxide semiconductor (CMOS) image sensors that read signal electric charge stored in a photodiode (photoelectric conversion element) through metal oxide semiconductor (MOS) transistors have been used in various applications in recent years. In general, CMOS image sensors have a substrate on which photodiodes that photoelectrically convert incident light are formed, and a wiring layer formed on the substrate. At present, as CMOS image sensors, front-illuminated CMOS image sensors that are irradiated with light from the surface on the wiring layer side of the substrate have been widely used. Furthermore, in recent years, in order to improve the sensitivity of photodiodes, back-illuminated CMOS image sensors that are irradiated with light from the surface (reverse surface) on a side opposite to the wiring layer side of the substrate also have been proposed.
In a back-illuminated CMOS image sensor, in virtue of its structural features, when compared to the front-illuminated CMOS image sensor, degree of freedom of layout of, for example, wires, transistors, and the like, which are provided in pixel units, is markedly improved. Specifically speaking, a front-illuminated CMOS image sensor is irradiated with light from the wiring layer side of the substrate. Consequently, phenomena, such as reflection, absorption, refraction, light-shielding, and the like of incident light, occur in, for example, wires, transistors, and the like of pixel units. For this reason, in the front-illuminated CMOS image sensor, the sensitivity of photodiodes may be decreased or sensitivity difference may occur between pixels. Therefore, in the front-illuminated CMOS image sensor, in order to solve such problems, it is necessary that a layout be devised in pixel units so that wiring is not arranged as much as possible on photodiodes.
On the other hand, since the back-illuminated CMOS image sensor is irradiated with light from the reverse surface of the substrate, the back-illuminated CMOS image sensor is not easily affected by reflection, absorption, refraction, and the like of incident light in wires, transistors, and the like of pixel units. In addition, since the back-illuminated CMOS image sensor is irradiated with light from the reverse surface of the substrate, it is possible to arrange the wiring of pixel units on photodiodes. Therefore, in the back-illuminated CMOS image sensor, when compared to the front-illuminated CMOS image sensor, the degree of freedom of layout increases.
Hitherto, in a CMOS image sensor, as the pixel size becomes finer, a technology of sharing pixels is often adopted so as to maximize the photodiode numerical aperture. In this pixel sharing technology, by sharing transistors among a plurality of pixels so as to minimize the occupation area of elements other than the photodiodes in the pixel units, the area of the photodiodes is secured. By using this pixel sharing technology, it is possible to improve characteristics, such as the amount of signal saturated and the sensitivity of photodiodes.
Accordingly, hitherto, in the CMOS image sensor in which the pixel sharing technology is applied, various pixel unit layouts have been proposed (for example, see Japanese Unexamined Patent Application Publication Nos. 2010-147965, 2010-212288, 2007-115994, and 2011-049446).
Japanese Unexamined Patent Application Publication No. 2010-147965 describes a front-illuminated CMOS image sensor in which four pixels are shared. In Japanese Unexamined Patent Application Publication No. 2010-147965, light-receiving areas formed by four photodiodes, which are arranged by 2×2 in the vertical arrangement direction and the horizontal arrangement direction of pixels (hereinafter, referred to as vertical direction and horizontal direction, respectively) are repeatedly arranged in a two-dimensional manner. Then, two pixels arranged in one of the diagonal directions in a predetermined first light-receiving area, and two pixels arranged in one of the diagonal directions in a second light-receiving area adjacent to one of the sides of the first light-receiving area in the vertical direction constitute one sharing unit.
Furthermore, in the CMOS image sensor of Japanese Unexamined Patent Application Publication No. 2010-147965, in the vertical direction, between the first light-receiving area and the second light-receiving area, a reset transistor and a contact hole that are shared by four pixels are arranged. Then, an amplification transistor and a selection transistor, which are shared in four pixels, are arranged between the first light-receiving area and a light-receiving area adjacent on a side opposite to the second light-receiving area side of the first light-receiving area.
Japanese Unexamined Patent Application Publication No. 2010-212288 describes a front-illuminated CMOS image sensor in which a plurality of pixels adjacent in the column direction are shared. Then, in the CMOS image sensor of Japanese Unexamined Patent Application Publication No. 2010-212288, a reset transistor is arranged in one of the diagonal directions of the photodiode of a predetermined pixel among a plurality of pixels that are shared, and an amplification transistor and a selection transistor are arranged on the other side.
Japanese Unexamined Patent Application Publication No. 2007-115994 describes a back-illuminated CMOS image sensor in which light-receiving areas formed of four photodiodes, which are arranged by 2×2 in the vertical direction and in the horizontal direction, are repeatedly arranged in a two-dimensional manner. Then, two pixels that are arranged in one of the diagonal directions in the predetermined first light-receiving area, and two pixels that are arranged in one of the diagonal directions in a second light-receiving area adjacent to one of sides of the first light-receiving area in the vertical direction constitute one sharing unit. Furthermore, in the CMOS image sensor of Japanese Unexamined Patent Application Publication No. 2007-115994, the reset transistor, the amplification transistor, and the selection transistor, which are shared by four pixels, are arranged between the first light-receiving area and the second light-receiving area.
Japanese Unexamined Patent Application Publication No. 2011-049446 describes a back-illuminated CMOS image sensor in which eight pixels are shared. In the CMOS image sensor of Japanese Unexamined Patent Application Publication No. 2011-049446, a first light-receiving unit in which four photodiodes are arranged by 2×2 in the vertical direction and in the horizontal direction and a second light-receiving unit having a structure similar to that of the first light-receiving unit constitute one sharing unit. Then, the second light-receiving unit is arranged so as to be adjacent to one of the sides of the first light-receiving unit in the vertical direction. Furthermore, in the CMOS image sensor of Japanese Unexamined Patent Application Publication No. 2011-049446, an amplification transistor shared by eight pixels is arranged between the first light-receiving unit and the second light-receiving unit, and a reset transistor is arranged between the first light-receiving unit and a light-receiving unit on a side opposite to the second light-receiving unit side of the first light-receiving unit.